1. Field of the Invention
The present invention relates to a main spindle device which grasps a collet.
2. Description of the Related Art
As a method of clamping a collet, conventional main spindle devices have utilized a method that involves the use of a member called toggle or damper. In this method, such a toggle or a damper is used for drawing a collet so that the collet constricts in diameter, or for pushing the collet so that the collet is loosen in diameter to unclamp a work. These methods will hereinafter be called “toggle method”.
Other than these, a method which utilizes the urging force of coned disc springs has also been proposed. This method will hereinafter be called “coned disc spring method”. For example, Unexamined Japanese Patent Application KOKAI Publication No. 2005-319540 discloses a main spindle device for a machine tool, which is of a coned disc spring method type.
However, each of the methods described above has problems that (1) the device is hard to rotate at a high speed, (2) reduction of the device size is difficult, and (3) fine adjustment of the chuck clamping force is difficult.
The toggle method suffers from (1) the device being hard to rotate at a high speed, because the device includes portions that easily lose their fine balance. Further, why (2) size reduction is difficult is because the main spindle has to be provided externally with devices such as an air cylinder, etc. by an add-on manner, thereby having a large size totally. Furthermore, a thin-walled pipe or the like is generally at a risk of being crushed, if grasped by the toggle method. This proves that (3) fine adjustment of the chuck clamping force is difficult.
In the coned disc spring method, on the other hand, why (1) high speed rotation is difficult is because no coned disc springs are provided near the collet and some portions therearound get out of balance easily. Further, (2) size reduction is difficult, because the coned disc springs themselves need to have a relatively long size to achieve a sufficient spring force. The existence of a piston bearing also makes size reduction difficult. Further, as regards the problem (3), it is possible to weaken the chuck clamping force by reducing the number of coned disc springs. However, it is generally difficult to finely adjust the clamping force of the chuck.
The present invention was made in view of the above-described circumstance, and an object of the present invention is to provide a main spindle device which can be rotated at a high speed while preventing sways of a work. Another object of the present invention is to provide a main spindle device which can be reduced in size.